Imaging device and imaging method having an illuminance calculation unit calculating respective illuminances corresponding to digital signals

ABSTRACT

An imaging device includes an exposure control unit, a determination unit, and an illuminance calculation unit. The exposure control unit is configured to control a plurality of exposure times. The determination unit is configured to determine whether or not saturation occurs using at least one data item of a plurality of data items obtained during the plurality of exposure times. The illuminance calculation unit is configured to calculate, if the determination unit determines that the saturation occurs, an illuminance using a data item different from the at least one data item used in the determination.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a Continuation Application of U.S. application Ser. No.14/051,636, filed Oct. 11, 2013, which claims priority to patentApplication JP 2012-245034 filed Nov. 7, 2012, the entire contents ofwhich are incorporated herein by reference.

BACKGROUND

The present disclosure relates to an imaging device and an imagingmethod. More particularly, the present disclosure relates to an imagingdevice and an imaging method that make it possible to calculate anilluminance with higher accuracy.

In recent years, miniaturization and higher functionality of a cellularphone, a digital camera, and the like are in progress. Power consumptionincreases due to the higher functionality, and hence measures are takento achieve low power consumption. With the progress of miniaturization,measures are taken to achieve miniaturization of the battery or thelike. In the cellular phone or the like, regarding the brightness of anLCD or key light, a high-luminance design is employed such that the LCDor the key light can be easily viewed also in a dark place. However,achieving high luminance increases power consumption. Therefore, aluminance sensor is provided. Based on a luminance data item determinedby the illuminance sensor, the luminance of the LCD or the key light isadjusted to optimize the illuminance. In this way, a reduction of powerconsumption is achieved.

However, for this purpose, it is necessary to install an illuminancesensor into a terminal. A position at which the illuminance sensor isinstalled has to be suitable for illuminance measurement, and hence hasa large constraint on mounting. Further, a design of a screen forreceiving light is also necessary, and hence it becomes a constraint onnot only mounting but also design. As techniques in the related art thatare aimed to implement functions of an illuminance sensor and a cameramodule with small space, there are cellular phones disclosed in JapanesePatent Application Laid-open No. 2003-110681, Japanese PatentApplication Laid-open No. 2008-042846, and Japanese Patent ApplicationLaid-open No. 2002-300447 (hereinafter, referred to as Patent Documents1, 2, and 3, respectively).

SUMMARY

As in the techniques described in Patent Documents 1 to 3, anilluminance can be detected based on a data item of a camera module.However, in illuminance detection for a single exposure time,illuminance calculation is performed also in a saturation state, forexample, and hence it can be difficult to perform illuminance detectionwith high accuracy.

In view of the above-mentioned circumstances, it is desirable to performilluminance detection with higher accuracy.

According to an embodiment of the present disclosure, there is providedan imaging device including: an exposure control unit configured tocontrol a plurality of exposure times; a determination unit configuredto determine whether or not saturation occurs using at least one dataitem of a plurality of data items obtained during the plurality ofexposure times; and an illuminance calculation unit configured tocalculate, if the determination unit determines that the saturationoccurs, an illuminance using a data item different from the at least onedata item used in the determination.

The determination unit may be configured to calculate an average valueof the plurality of data items and determine, based on a comparisonresult between the average value and a threshold value, whether or notsaturation occurs.

The determination unit may be configured to calculate an average valueof data items obtained during a first exposure time and determines, ifthe average value is equal to or larger than a threshold value, that thesaturation occurs, and the illuminance calculation unit may beconfigured to obtain, if the determination unit determines that thesaturation occurs, a data item obtained during a second exposure timeshorter than the first exposure time, and calculate an illuminance.

The imaging device may further include: a comparator configured tocompare each of the plurality of data items with a first thresholdvalue; and a count unit configured to count the number of comparisonresults of comparison results from the comparator, each of whichsatisfies a predetermined condition. The determination unit may beconfigured to determine, based on a comparison result between a countvalue of the count unit and a second threshold value, whether or notsaturation occurs.

The imaging device may further include: a comparator configured tocompare each of data items obtained during a first exposure time with afirst threshold value; and a count unit configured to count the numberof comparison results of comparison results from the comparator, in eachof which the data item is equal to or larger than the first thresholdvalue. The determination unit may be configured to determine, if a countvalue of the count unit is equal to or larger than a second thresholdvalue, that the saturation occurs, and the illuminance calculation unitmay be configured to obtain, if the determination unit determines thatthe saturation occurs, a data item obtained during a second exposuretime shorter than the first exposure time, and calculate an illuminance.

The imaging device may further include: a comparator configured tocompare each of the plurality of data items with a first thresholdvalue; an output unit configured to output, as a comparison result fromthe comparator, codes each indicating a comparison result between thedata item and the first threshold value; and a count unit configured tocount the number of codes of the codes from the output unit, each ofwhich satisfies a predetermined condition. The determination unit may beconfigured to determine, based on a comparison result between a countvalue of the count unit and a second threshold value, whether or notsaturation occurs.

The imaging device may further include: a comparator configured tocompare each of data items obtained during a first exposure time with afirst threshold value; an output unit configured to output, as acomparison result from the comparator, codes each indicating whether ornot the data item is equal to or larger than the first threshold value;and a count unit configured to count the number of codes of the codesfrom the output unit, each of which indicates that the data item isequal to or larger than the first threshold value. The determinationunit may be configured to determine, if a count value of the count unitis equal to or larger than a second threshold value, that the saturationoccurs, and the illuminance calculation unit may be configured toobtain, if the determination unit determines that the saturation occurs,a data item obtained during a second exposure time shorter than thefirst exposure time, and calculate an illuminance.

According to another embodiment of the present disclosure, there isprovided an imaging method for an imaging device including an exposurecontrol unit, a determination unit, and an illuminance calculation unit,the method including: controlling, by the exposure control unit, aplurality of exposure times; determining, by the determination unit,whether or not saturation occurs using at least one data item of aplurality of data items obtained during the plurality of exposure times;and calculating, by the illuminance calculation unit, if thedetermination unit determines that the saturation occurs, an illuminanceusing a data item different from the at least one data item used in thedetermination.

In the imaging apparatus and the imaging method according to theembodiments of the present disclosure, the plurality of exposure timesare controlled, whether or not saturation occurs is determined using theat least one data item of the plurality of data items obtained duringthe plurality of exposure times, and, if it is determined that thesaturation occurs, the illuminance is calculated using the data itemdifferent from the at least one data item used in the determination.

According to the embodiments of the present disclosure, it becomespossible to perform illuminance detection with higher accuracy.

These and other objects, features and advantages of the presentdisclosure will become more apparent in light of the following detaileddescription of best mode embodiments thereof, as illustrated in theaccompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing a configuration of a solid-state imagingdevice according to a first embodiment to which the present disclosureis applied;

FIG. 2 is a timing chart for describing an operation of ananalog-to-digital converter (ADC);

FIG. 3 is a flowchart for describing determination processing associatedwith illuminance calculation;

FIGS. 4A to 4C are diagrams for describing saturation;

FIG. 5 is a diagram showing a configuration of a solid-state imagingdevice according to a second embodiment;

FIG. 6 is a flowchart for describing determination processing associatedwith illuminance calculation in the second embodiment;

FIG. 7 is a diagram for describing determination processing associatedwith the illuminance calculation;

FIGS. 8A to 8C are diagrams for describing saturation;

FIG. 9 is a diagram showing a configuration of a solid-state imagingdevice according to a third embodiment;

FIG. 10 is a diagram showing a configuration of the solid-state imagingdevice according to the third embodiment;

FIG. 11 is a flowchart for describing determination processingassociated with illuminance calculation in the third embodiment;

FIG. 12 is a diagram for describing determination processing associatedwith the illuminance calculation;

FIG. 13 is a diagram showing a configuration of a solid-state imagingdevice according to a fourth embodiment;

FIG. 14 is a diagram showing a configuration of a back-side-illuminationsolid-state imaging device;

FIG. 15 is a diagram showing a configuration of an imaging apparatus;and

FIG. 16 is a diagram for describing a recording medium.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments for carrying out of the present disclosure(hereinafter, referred to as embodiments) will be described. Note thatdescriptions will be made in the following order.

1. First Embodiment

2. Second Embodiment

3. Third Embodiment

4. Fourth Embodiment

5. Application to Back Side Illumination

6. Configuration of Imaging Apparatus

7. Recording Medium

First Embodiment

FIG. 1 is a diagram showing a configuration of a solid-state imagingdevice 100 according to an embodiment to which the present disclosure isapplied. Specifically, FIG. 1 is a block diagram showing an exemplaryconfiguration of a column-parallel analog-to-digital converter(ADC)-installed solid-state imaging device (complementary metal-oxidesemiconductor (CMOS) image sensor) used as the solid-state imagingdevice 100.

The solid-state imaging device 100 shown in FIG. 1 includes a pixel unit101, an ADC 102, a horizontal transfer scanning circuit 103, adigital-to-analog converter (DAC) 104, a vertical scanning circuit 105,an arithmetic control unit 106, an output control circuit 107, and anoutput control circuit 108.

The pixel unit 101 includes unit pixels 121 arranged in a matrix form.Each of the unit pixels 121 includes a photodiode (photoelectricconversion element) and an amplifier in the pixel. Regarding the pixelunit 101, pixel driving lines (not shown) are formed for each row alongleft- and right-hand directions of the figure (arraying direction ofpixels in pixel row) in the pixel arrangement in the matrix form, andvertical signal lines 122-1 to 122-N are formed for each column along inupper and lower directions of the figure (arraying direction of pixelsin pixel column. Note that, in the following description, when it isunnecessary to distinguish between the vertical signal lines 122-1 to122-N, the vertical signal lines 122-1 to 122-N will be simply referredto as vertical signal lines 122. The same will apply hereinafter.

The vertical scanning circuit 105 is a pixel drive unit that includes ashift register, an address decoder, and the like and drives pixels ofthe pixel unit 101, for example, at the same time or on the row basis.Although an illustration of a specific configuration of the verticalscanning circuit 105 is omitted, the vertical scanning circuit 105includes a read-scanning system and a sweep-scanning system or includesa configuration having a batch sweep function and a batch transferfunction.

Pixel signals output from unit pixels of a pixel row selected andscanned by the vertical scanning circuit 105 are supplied to ADCs 102-1to 102-N through the vertical signal lines 122-1 to 122-N, respectively.The ADC 102 performs, for each pixel column of the pixel unit 101,predetermined signal processing on pixel signals output from unit pixelsin a selected row through the vertical signal line 122. The processedpixel signals are supplied to the horizontal transfer scanning circuit103. The processing in the ADC 102 will be described later withreference to FIG. 2.

The horizontal transfer scanning circuit 103 includes a shift register,an address decoder, and the like, and sequentially selects unit circuitsof the ADCs 102-1 to 102-N corresponding to the pixel columns. Due tothe selection and scanning of the horizontal transfer scanning circuit103, the pixel signals subjected to the signal processing in the ADC 102are sequentially output to the arithmetic control unit 106.

Now, referring to FIG. 2, the processing in the ADC 102 will bedescribed. The ADC 102 includes a comparator 141 and a counter 142. FIG.2 is a timing chart of the ADC 102. In the ADC 102 shown in FIG. 1,sweeping of a reference voltage Vramp from the DAC 104 starts at thecomparator 141, and, at the same time, a count operation of the counter142 starts. When the reference voltage Vramp drops below an inputvoltage VSL, an output signal VCO of the comparator 141 is reversed froma high level to a low level. This falling edge stops the count operationof the counter 142. A count value VCNT is in a one-to-one relation witha voltage width of the reference voltage Vramp swept. The count valueVCNT is a result of analog-to-digital (AD) converting an input voltage.

Data items from the ADC 102 are provided to the arithmetic control unit106 by the processing of the horizontal transfer scanning circuit 103.The arithmetic control unit 106 has a configuration including an imagesignal processing unit 161, a data selector 162, an illuminancecalculation unit 163, a determination unit 164, and an exposure controlunit 165. The image signal processing unit 161 processes a data itemfrom the horizontal transfer scanning circuit 103, generates an imagesignal, and outputs the image signal to the output control circuit 108.The data item from the horizontal transfer scanning circuit 103 isprovided also to the data selector 162 and the determination unit 164.

The data selector 162 selects a data item corresponding to adetermination result of the determination unit 164 and outputs the dataitem to the illuminance calculation unit 163. The determination unit 164determines which of a long-term stored data item and a short-term storeddata item is to be selected, and outputs a determination result to thedata selector 162 and the exposure control unit 165. The long-termstored data item is a first digital electrical signal outputcorresponding to a first exposure time. The short-term stored data itemis a second digital electrical signal output corresponding to a secondexposure time. The first exposure time is set to be longer than thesecond exposure time.

The long-term stored data item is a data item obtained when long-termexposure is performed. The short-term stored data item is a data itemobtained when short-term exposure is performed. The first exposure timeand the second exposure time may be fixed or may be varied depending ona predetermined condition.

The determination unit 164 generates, from the supplied long-term storeddata item and short-term stored data item, a data item by apredetermined operation, and determines, based on the data item, whetheror not a saturation state occurs. The determination unit 164 outputs anexposure time during which it is determined that the saturation statedoes not occur, as a determination result. A data item corresponding tothe exposure time during which it is determined that the saturationstate does not occur is selected by the data selector 162 and output tothe illuminance calculation unit 163. The illuminance calculation unit163 calculates an illuminance using the long-term stored data item orshort-term stored data item selected by the data selector 162, andoutputs the illuminance to the output control circuit 107.

The illuminance is calculated based on Expression (1) below.Illuminance=(long-term stored data item or short-term stored dataitem[LSB]×1LSB voltage[mV/LSB])/(sensitivity[mv/(lux-s)]×long storagetime or short storage time[s])   (1)In Expression (1), a selected data item is used in the “long-term storeddata item or short-term stored data item” and a storage time (exposuretime) corresponding to the selected data item is used in the “longstorage time or short storage time.”

The determination result of the determination unit 164 is supplied alsoto the exposure control unit 165 and used for exposure control, forexample, control to perform short-term exposure or long-term exposure.The exposure control unit 165 controls the vertical scanning circuit 105and controls a read-out timing in a vertical direction.

As the first embodiment, an embodiment in which a determination of thedetermination unit 164 is performed by calculating an average value ofthe supplied long-term stored data item or short-term stored data itemwill be exemplified and described. FIG. 3 is a flowchart for describingprocessing associated with the calculation of the illuminance.

In Step S101, the determination unit 164 obtains the long-term storeddata item. The long-term stored data item is a data item relating to theamount of charge accumulated in each unit pixel 121 during exposure forthe first exposure time. Data items relating to the amount of charge maybe obtained from all the unit pixels 121 constituting the pixel unit101. However, data items relating to the amount of charge may beobtained in a thinning-out state.

For example, not all the pixel row but the thinned-out pixel rows may bevertically scanned and outputs depending on the amount of incident lightmay be transmitted from the scanned pixel rows to the vertical signalline 122 of each column. The thinned-out pixel rows are verticallyscanned, and hence power consumption can be reduced and the capacity ofa buffer for temporarily storing data items in order to determine anaverage value can be reduced. In addition, the amount of data item isreduced, and hence the processing capacity can be saved.

In the case where the thinned-out data items described above areobtained, when a data item for calculating an illuminance is obtained,the exposure control unit 165 controls the vertical scanning circuit 105based on an instruction from the determination unit 164 such that suchread-out is performed. The determination unit 164 issues an instructionto the exposure control unit 165 during the illuminance calculation.This enables the exposure control unit 165 to switch between controllingread-out during the illuminance calculation and controlling read-out forobtaining an image signal.

In Step S102, the determination unit 164 calculates an average valuefrom long-term stored data items. Whether or not the average valuecalculated in Step S102 exceeds a value upon saturation (thresholdvalue) is determined, to thereby determine whether or not the saturationstate occurs during the long-term exposure.

In Step S103, the determination unit 164 determines whether or notsaturation occurs. In Step S103, if it is determined that the saturationdoes not occur, that is, if it is determined that the saturation doesnot occur due to the long-term exposure, the processing proceeds to StepS104. In Step S104, the long-term stored data item is selected.

The determination unit 164 notifies the data selector 162 of theselection of the long-term stored data item. Then, the data selector 162selects the long-term stored data item and outputs the selectedlong-term stored data item to the illuminance calculation unit 163.

The illuminance calculation unit 163 obtains, in Step S106, thelong-term stored data item selected by the data selector 162 and output,and calculates, based on Expression (1) above, an illuminance. Theilluminance is output to the output control circuit 107.

Otherwise, in Step S103, it is determined that the saturation occurs,that is, if it is determined that the saturation occurs due to thelong-term exposure, the processing proceeds to Step S105. In Step S105,the short-term stored data item is selected.

The determination unit 164 notifies the data selector 162 of theselection of the short-term stored data item. The data selector 162selects the short-term stored data item and outputs the short-termstored data item to the illuminance calculation unit 163. If theshort-term stored data item is configured to be supplied after thelong-term stored data item is supplied to the data selector 162, theshort-term stored data item may be obtained while a determination ismade by the determination unit 164 based on the long-term stored dataitem, and the short-term stored data item may be selected.

The illuminance calculation unit 163 obtains, in Step S106, theshort-term stored data item selected in the data selector 162 andoutput, and calculates an illuminance based on Expression (1) above. Theilluminance is output to the output control circuit 107.

Although the average value is calculated from the long-term stored dataitems and whether or not saturation occurs due to the long-term exposureis determined in the above description, an average value may becalculated from short-term stored data items and a determination may bemade. In the case where an average value is calculated from short-termstored data items and a determination is made, whether or not thecalculated average value is smaller than a predetermined threshold valueis determined.

If the average value is smaller than the predetermined threshold value,it is determined that the exposure time is short, and, since the outputis insufficient, the long-term stored data item obtained during thelong-term exposure is selected. Otherwise, if the average value islarger than the predetermined threshold value, it is determined that theexposure time is sufficient and the short-term stored data item obtainedduring the short-term exposure is selected. In this manner, even in thecase where the average value of the short-term stored data items isused, whether or not the exposure time is appropriate can be performedand a determination as to the selection of the long-term stored dataitem or the short-term stored data item can be made.

Further, in the case where an average value is calculated fromshort-term stored data items and a determination is made, by supplying along-term stored data item after a short-term stored data item issupplied to the data selector 162, the data selector 162 can obtain thelong-term stored data item after the determination unit 164 makes adetermination based on the short-term stored data item as in theabove-mentioned case.

Although the average value is calculated from the long-term stored dataitems or the short-term stored data items and the determination is madein the above description, an average value of long-term stored dataitems and an average value of short-term stored data items may becalculated and determinations may be made.

For example, such a configuration can also address a situation where itis determined that the saturation occurs due to the long-term exposurebecause the average value calculated from the long-term stored dataitems is larger than a predetermined value and it is determined that theexposure time of the short-term exposure is insufficient because theaverage value calculated from the short-term stored data items issmaller than the predetermined value. If such a situation occurs, acontrol to use an exposure time between the long-term exposure and theshort-term exposure (first exposure time and second exposure time) canbe performed. Thus, a finer illuminance control can be performed.

In this manner, the average value is calculated from the long-termstored data items or the short-term stored data items and whether or notsaturation occurs is determined, and hence an appropriate illuminancecan be calculated and a control based on the appropriate illuminance canbe performed.

Although two data items of the long-term stored data item and theshort-term stored data item are used in the above description, aplurality of data items may be used. In this case, the exposure controlunit 165 is configured to be capable of controlling a plurality ofexposure times and the determination unit 164 is configured to obtaindata items when a control is performed during one exposure time of theplurality of exposure times.

The determination unit 164 calculates an average value from the obtaineddata items and determines whether or not saturation occurs due to theexposure time during which the data item is obtained. Depending on adetermination result, for example, if it is determined that thesaturation occurs, such that an illuminance is calculated using adifferent data item, the data selector 162 is configured to select thedata item and output the data item to the illuminance calculation unit163.

Further, the exposure control unit 165 is configured to control exposuretimes such that the data selector 162 can select a different data itemand the illuminance calculation unit 163 can calculate an illuminanceusing the different data item.

In this manner, the exposure control unit 165 may be capable ofcontrolling a plurality of exposure times and the determination unit 164may determine whether or not saturation occurs using at least one dataitem of a plurality of data items obtained during the plurality ofexposure times. Further, if it is determined that the saturation occurs,the data selector 162 may be configured to select another data itemassumed to have been obtained without saturation (data item differentfrom data item used in determination), and the illuminance calculationunit 163 may be configured to calculate an illuminance based on theselected data item.

In the case where the above-mentioned average value is calculated andwhether or not saturation occurs is determined based on the averagevalue, even if pixels exceeding a saturation level under a particularcondition are present, there is a possibility that the long-term storeddata item is selected and a determination is made. Referring to FIGS. 4Ato 4C, a case where pixels exceeding a saturation level under aparticular condition will be described.

Graphs shown in FIGS. 4A to 4C are graphs relating to an incident lightdistribution. In FIGS. 4A to 4C, thick straight solid lines indicate asaturation level and thin straight solid lines indicate a thresholdvalue, straight dotted lines indicate an average value, and a curvesolid lines indicate a distribution of long-term stored data items beingdata items from which an average value is calculated.

FIGS. 4A to 4C show a case where the average value is smaller than thethreshold value, the long-term stored data item is selected as the dataitem for the illuminance calculation. In such a case and in the casewhere all the long-term stored data items are below the saturation levelas shown in FIG. 4A, selecting the long-term stored data item andcalculating an illuminance based on the long-term stored data item arecorrect processing.

As shown in FIG. 4B, even in the case where some of long-term storeddata items exceed the saturation level, if others are below thesaturation level, an average value of the long-term stored data items isequal to or smaller than the threshold value in some cases. For example,in the case of a local-light-source image in which a light source isincluded in part of the image and the light source is bright but thesurroundings of the light source are dark, there is a possibility thatthe state as shown in FIG. 4B is obtained.

Further, for example, in the case of a gradation image the brightness ofwhich gradually increases, as shown in FIG. 4C, there is a possibilitythat some of long-term stored data items exceed the saturation level.

Even in the cases of the states shown in FIGS. 4B and 4C, the averagevalue is equal to or smaller than the threshold value, and hence thelong-term stored data item is selected and an illuminance is calculatedbased on the long-term stored data item. In such cases, the accuracy ofthe illuminance calculation lowers. In order to calculate an illuminancewith high accuracy when the local-light-source image and the gradationimage are captured, an embodiment in which a determination is made usinga data item other than an average value will be described below.

Second Embodiment

FIG. 5 is a diagram showing a configuration of a solid-state imagingdevice 200 according to a second embodiment. The solid-state imagingdevice 200 shown in FIG. 5 includes a pixel unit 101, an ADC 102, ahorizontal transfer scanning circuit 103, a DAC 104, a vertical scanningcircuit 105, an output control circuit 107, an output control circuit108, and an arithmetic control unit 201.

Comparing the solid-state imaging device 200 shown in FIG. 5 with thesolid-state imaging device 100 shown in FIG. 1, a configuration of thearithmetic control unit 201 is different from the arithmetic controlunit 106 shown in FIG. 1 and other parts are the same. The same parts asthose of the solid-state imaging device 100 shown in FIG. 1 will bedenoted by the same reference symbols and descriptions thereof will beappropriately omitted.

The arithmetic control unit 201 includes an image signal processing unit202, a data selector 203, an illuminance calculation unit 204, and asaturation determination unit 205. The saturation determination unit 205includes a switch 211, a digital comparator 212, a counter 213, and adetermination unit 214.

A long-term stored data item or a short-term stored data item issupplied from the horizontal transfer scanning circuit 103 to the dataselector 203 of the arithmetic control unit 201 and to the digitalcomparator 212 via the switch 211. The digital comparator 212 issupplied with a reference voltage Vref. The reference voltage Vref iscompared with the long-term stored data item or the short-term storeddata item. In the following description, it is assumed that thelong-term stored data item is compared.

The counter 213 counts, out of data items output from the digitalcomparator 212, the number of data items in which it is determined thatthe long-term stored data item is larger than the reference voltageVref. The determination unit 214 determines whether or not the valuecounted by the counter 213 is equal to or larger than a threshold value.For example, the threshold value in the determination unit 214 is set tobe 5% of the number of pixels outputting the long-term stored data item.

The long-term stored data item can be a data item relating to the amountof charge accumulated during exposure for the first exposure time ineach unit pixel 121. Alternatively, not all pixel rows but thinned-outpixel rows may be vertically scanned and outputs depending on the amountof incident light may be transmitted from the scanned pixel rows to thevertical signal line 122 of each column.

In the case where the thinned-out data items are obtained, when a dataitem for calculating an illuminance is obtained, an exposure controlunit 206 controls the vertical scanning circuit 105 based on aninstruction from the determination unit 214 such that such read-out isperformed. The determination unit 214 issues an instruction to theexposure control unit 206 during the illuminance calculation. Thisenables the exposure control unit 206 to switch between controllingread-out during the illuminance calculation and controlling read-out forobtaining an image signal.

Although shown in FIG. 5, signal lines for issuing an instruction ofsuch switching are provided from the determination unit 214 to theexposure control unit 206. Alternatively, a signal for such switchingmay be supplied from a controller (not shown) to the exposure controlunit 206.

Referring to a flowchart of FIG. 6, processing associated withcalculation of an illuminance in the solid-state imaging device 200 willbe described. In Step S201, N=N+1 is set. An initial value of N is 0,which is a value for identifying a pixel to be processed. For example,numbers are assigned to pixels from an upper left pixel to a lower rightpixel of the pixel unit 101. When the value of N becomes one of thenumbers, a data item of the pixel assigned with the number is set as aprocessing target.

In Step S202, whether or not an Nth long-term stored data item is equalto or larger than the threshold value is determined. The digitalcomparator 212 outputs a plus value if the input Nth long-term storeddata item is equal to or larger than the reference voltage Vref(threshold value), and outputs a minus value if the input Nth long-termstored data item is smaller than the threshold value. The counter 213determines, if the digital comparator 212 outputs the plus value, thatthe long-term stored data item as the processing target is equal to orlarger than the threshold value, and determines, if the digitalcomparator 212 outputs the minus value, that the long-term stored dataitem as the processing target is smaller than the threshold value.

The reference voltage Vref is set to be a value smaller than thesaturation level value and highly likely to cause saturation beyond thevalue, and is used as the threshold value for determining whether or notsaturation occurs. The threshold value used in the digital comparator212 is set as, for example, a value of 90% of the saturation level. Thethreshold value may be fixed or may be varied. Note that 90% is anexample and should not be construed as limiting.

If it is determined in Step S202 that the long-term stored data item asthe processing target is equal to or larger than the threshold value,the processing proceeds to Step S203. In Step S203, the counter 213updates the value to a value obtained by incrementing a counter value byone.

After the processing of Step S203 or in Step S202, if it is determinedthat the long-term stored data item as the processing target is notequal to or larger than the threshold value, the processing proceeds toStep S204.

In Step S204, whether or not N reaches the number of pixels as theprocessing target is determined. In Step S204, if it is determined thatthe N=target number of pixels is not established, the processing returnsto Step S201 and the subsequent processing is performed again.Specifically, a subsequent pixel is set as the processing target andwhether or not the subsequent pixel is equal to or larger than thethreshold value is determined.

Otherwise, in Step S204, it is determined that N=target number of pixelsis established, the processing proceeds to Step S205. In Step S205, thedetermination unit 214 determines whether or not the count value countedby the counter 213 is equal to or larger than the threshold value. Thethreshold value in the determination unit 214 is set to be, for example,the number of pixels as the processing target, in other words, 5% of thetarget number of pixels when it is determined that N=target number ofpixels is established in the processing in Step S204.

Note that 5% is an example, should not be construed as limiting, and isset considering properties or the like of the unit pixels 121.Alternatively, the threshold value in the determination unit 214 may befixed or varied.

In Step S205, if it is determined that the count value is not equal toor larger than the threshold value, the processing proceeds to StepS206. In Step S206, the long-term stored data item is selected. In thiscase, it is determined that the saturation does not occur due to thelong-term exposure, and hence the processing proceeds to Step S206 andthe long-term stored data item is selected.

The determination unit 214 notifies the data selector 203 of theselection of the long-term stored data item. The data selector 203selects the long-term stored data item and outputs the long-term storeddata item to the illuminance calculation unit 204. In Step S208, theilluminance calculation unit 204 obtains a long-term stored data itemselected by the data selector 203 and output, and calculates anilluminance based on Expression (1) above and outputs the illuminance tothe output control circuit 107.

Otherwise, in Step S205, it is determined that the count value is equalto or larger than the threshold value, that is, if it is determined thatthe saturation occurs due to the long-term exposure, the processingproceeds to Step S207. In Step S207, the short-term stored data item isselected.

The determination unit 214 notifies the data selector 203 of theselection of the short-term stored data item. The data selector 203selects the short-term stored data item and outputs the short-termstored data item to the illuminance calculation unit 204. In Step S208,the illuminance calculation unit 204 obtains the short-term stored dataitem selected by the data selector 203 and output, and calculates anilluminance based on Expression (1) above and outputs the illuminance tothe output control circuit 107.

Note that, in the above description, the long-term stored data item iscompared with the threshold value (hereinafter, referred to as firstthreshold value), the number of data items each having a value equal toor larger than the first threshold value is counted, whether or not thecount value is equal to or larger than the threshold value (hereinafter,referred to as second threshold value) is determined, and thus whetheror not saturation occurs due to the long-term exposure is determined.

However, a determination may be made based on not the long-term storeddata item but the short-term stored data item. In the case where theshort-term stored data item is compared with a third threshold value,whether or not the short-term stored data item is equal to or smallerthan the third threshold value.

If it is determined that the short-term stored data item is equal to orsmaller than the third threshold value and a counted count value isequal to or lager than a fourth threshold value, it is determined thatthe exposure time is short and, since the output is insufficient, thelong-term stored data item obtained during the long-term exposure isselected.

Otherwise, if the count value is smaller than the fourth thresholdvalue, it is determined that the exposure time is sufficient and theshort-term stored data item obtained during the short-term exposure isselected. In this manner, even in the case where the count valueobtained from the short-term stored data item is used, whether or notthe exposure time is appropriate can be determined and a determinationassociated with the selection of the long-term stored data item or theshort-term stored data item can be made.

Now, referring to FIG. 7, the processing associated with the calculationof the illuminance in the solid-state imaging device 200 will bedescribed again. A point of time T1 to a point of time T2 correspond tothe first exposure time (long storage time). A data item when exposureis performed for the first exposure time is obtained by the saturationdetermination unit 205 (FIG. 5). In the saturation determination unit205, the processing in Steps S201 to S204 is repeated, and hence thenumber of values exceeding the threshold value in the digital comparator212 is counted.

At the point of time T2, a determination is made by the determinationunit 214. This processing corresponds to the processing in Step S205. Asthe result of the determination made at the point of time T2, which ofthe long-term stored data item and the short-term stored data item is tobe selected is determined. A point of time T3 to a point of time T4correspond to the second exposure time (short storage time) and a dataitem when exposure is performed for the second exposure time is obtainedif necessary.

If the determination unit 214 determines that the long-term stored dataitem is to be selected, the data selector 203 selects the long-termstored data item (corresponding to processing in Step S206). Thelong-term stored data item selected by the data selector 203 at thistime may be a long-term stored data item obtained during the firstexposure time from the point of time T1 to the point of time T2 or maybe a long-term stored data item obtained during the first exposure timefrom a point of time T5 to a point of time T6.

Otherwise, if the determination unit 214 determines that the short-termstored data item is to be selected, the data selector 203 selects theshort-term stored data item (corresponding to processing in Step S207).The short-term stored data item selected by the data selector 203 atthis time is a short-term stored data item obtained during the secondexposure time from the point of time T3 to the point of time T4.

The illuminance calculation unit 204 calculates an illuminance based onthe long-term stored data item or the short-term stored data item andoutputs the illuminance (corresponding to processing in Step S208).

The illuminance is output at, for example, the point of time T6. At thepoint of time T6, both of the long-term stored data item and theshort-term stored data item are already obtained, and hence theilluminance can be calculated even if either one of the long-term storeddata item and the short-term stored data item is selected.

Note that, if the long-term stored data item is selected, the obtentionof the short-term stored data item that is performed between the pointof time T3 and the point of time T4 may be omitted. If the long-termstored data item is selected and the long-term stored data item obtainedbetween the point of time T1 and the point of time T2 is used for theilluminance calculation, the illuminance may be calculated and outputbetween the point of time T2 and the point of time T3.

In the example shown in FIG. 7, the long-term stored data item obtainedduring the first exposure time from the point of time T1 to the point oftime T2 and the short-term stored data item obtained during the secondexposure time from the point of time T3 to the point of time T4 arepaired. However, for example, the short-term stored data item obtainedduring the second exposure time from the point of time T3 to the pointof time T4 and the long-term stored data item obtained during the firstexposure time from the point of time T5 to the point of time T6 may bepaired.

In this manner, the long-term stored data item exceeding the firstthreshold value is counted and whether or not the counted count valueexceeds the second threshold value is determined, to thereby determinewhether or not the saturation state occurs, and thus the illuminance canbe calculated with higher accuracy. Now, referring to FIGS. 8A to 8C, adescription will be added to the capability of calculating anilluminance without using a data item obtained when the saturationoccurs.

FIGS. 8A to 8C are graphs relating to an incident light distribution asin the graphs shown in FIGS. 4A to 4C. As in FIGS. 4A to 4C, in FIGS. 8Ato 8C, thick straight solid lines indicate a saturation level, thinstraight solid lines indicate a first threshold value, and a curve solidlines indicate a distribution of long-term stored data items comparedwith the first threshold value.

In FIGS. 8A to 8C, in portions in which ellipses are drawn, thelong-term stored data items exceed the first threshold value. If thenumber of data items exceeding the first threshold value is not largerthan a second threshold value in the determination unit 214, thelong-term stored data item is selected. If the number of data itemsexceeding the first threshold value is larger than the second thresholdvalue, the short-term stored data item is selected. The second thresholdvalue is set to be, for example, 5% of the number of long-term storeddata items.

As described above with reference to FIG. 4B, in the case where thelocal-light-source image is captured, there is a possibility that pixelsin part of the image are in the saturation state. Even in the case wheresuch a local light source is present, as shown in FIG. 8B, if the numberof data items exceeding the first threshold value is equal to or largerthan the second threshold value, it is determined that the long-termstored data item is obtained when the saturation occurs and thelong-term stored data item can be prevented from being used for theilluminance calculation. Thus, it is possible to prevent the calculationof an illuminance using the data item exceeding the saturation level.

Further, as described above with reference to FIG. 4C, also in the casewhere a gradation image the brightness of which gradually increases,there is a possibility that pixels in part of the image are in thesaturation state. Even in the case where such gradation is present, asshown in FIG. 8C, if the number of data items exceeding the firstthreshold value is equal to or larger than the second threshold value,it is determined that the long-term stored data item is obtained whenthe saturation occurs and the long-term stored data item can beprevented from being used for the illuminance calculation. Thus, it ispossible to prevent the calculation of an illuminance using the dataitem exceeding the saturation level.

In this manner, the long-term stored data item exceeding the firstthreshold value is counted and whether or not the counted count value islarger than the second threshold value is determined to determinewhether or not the saturation state occurs, and thus the illuminance canbe calculated with higher accuracy. Further, a configuration forcounting the long-term stored data items exceeding the first thresholdvalue can be simplified and low power consumption can be realized.

Although the two data items of the long-term stored data item and theshort-term stored data item are used in the above description, aplurality of data items may be used. In this case, the exposure controlunit 206 is configured to be capable of controlling a plurality ofexposure times and the digital comparator 212 is configured to obtaindata items when a control is performed during one exposure time of theplurality of exposure times.

A comparison result from the digital comparator 212 is supplied to thecounter 213 and the number of data items satisfying a predeterminedcondition, for example, a condition that the number of data items isequal to or larger than a threshold value as in the above-mentioned caseis counted. Based on the count value, the determination unit 214determines whether or not saturation occurs due to the exposure timeduring which the data item is obtained. Depending on a determinationresult, for example, when it is determined that the saturation occurs,such that an illuminance is calculated by using a different data item,the data selector 203 is configured to select the data item and outputthe data item to the illuminance calculation unit 204.

In this manner, the exposure control unit 206 may be configured to becapable of controlling the plurality of exposure times and thedetermination unit 214 may be configured to determine whether or notsaturation occurs using at least one data item of the plurality of dataitems obtained from the plurality of exposure times. Further, if it isdetermined that the saturation occurs, the data selector 203 may beconfigured to select another data item assumed to have been obtainedwithout saturation (data item different from data item used indetermination), and the illuminance calculation unit 204 may beconfigured to calculate an illuminance based on the selected data item.

Third Embodiment

FIG. 9 is a diagram showing a configuration of a solid-state imagingdevice 300 according to a third embodiment. The solid-state imagingdevice 300 shown in FIG. 5 includes a pixel unit 101, a horizontaltransfer scanning circuit 103, a vertical scanning circuit 105, anoutput control circuit 107, an output control circuit 108, a DAC 310, acounter controller 320, an ADC 330, and an arithmetic control unit 340.

Comparing the solid-state imaging device 300 shown in FIG. 9 with thesolid-state imaging device 100 shown in FIG. 1, configurations of thepixel unit 101, the horizontal transfer scanning circuit 103, thevertical scanning circuit 105, the output control circuit 107, and theoutput control circuit 108 of the solid-state imaging device 300 are thesame as those of the solid-state imaging device 100, and hence the sameportion as those of the solid-state imaging device 100 will be denotedby the same reference symbols and descriptions thereof will beappropriately omitted.

The DAC 310 includes a Vslop 311, a Vcons 312, and a switch 313. Thecounter controller 320 includes a 10-bit count 321, a 1-bit count 322,and a switch 323. The ADC 330 includes a comparator 331 and a counter332.

When an image signal is output from the output control circuit 108 ofthe solid-state imaging device 300, as shown in FIG. 10, the switch 313of the DAC 310 is connected to the Vslop 311. Further, as shown in FIG.10, the switch 323 of the counter controller 320 is connected to the10-bit count 321.

When an image signal is generated, a signal of the reference voltageVramp described above with reference to FIG. 2 is generated from theVslop 311 of the DAC 310 and is supplied to comparators 331-1 to 331-Nof ADCs 330-1 to 330-N. Further, a control signal for instructing toperform a 10-bit output is supplied from the 10-bit count 321 of thecounter controller 320 to counters 332-1 to 332-N of the ADCs 330-1 to330-N.

Otherwise, when an illuminance signal is output from the output controlcircuit 107 of the solid-state imaging device 300, as shown in FIG. 9,the switch 313 of the DAC 301 is connected to the Vcons 312. Further, asshown in FIG. 9, the switch 323 of the counter controller 320 isconnected to the 1-bit count 322.

When the illuminance signal is generated, a constant voltage Vcons isgenerated from the Vcons 312 of the DAC 310 and supplied to thecomparators 331-1 to 331-N of the ADCs 330-1 to 330-N. Further, acontrol signal for instructing to perform a 1-bit output is suppliedfrom the 1-bit count 322 of the counter controller 320 to the counters332-1 to 332-N of the ADCs 330-1 to 330-N.

The following description relates to the generation of the illuminancesignal, and hence the description will be continued with reference tothe block diagram of the solid-state imaging device 300 shown in FIG. 9.Here, it is assumed that, during the first exposure time (long-termstorage), the long-term stored data item for the illuminance calculationis obtained and the switch 313 and the switch 323 are connected in thestate as shown in FIG. 9.

As an operation of the ADC 330 during the first exposure time (long-termstorage), the constant voltage Vcons from the Vcons 312 of the DAC 310is input to one side of the comparator 331 and an input voltage Vs1 fromthe unit pixels 121 via the vertical signal line 122 is input to theother side. The constant voltage Vcons is used as a reference voltageand the reference voltage is used as a threshold value. Further, thereference voltage is an analog voltage corresponding to the referencevoltage Vref (digital) of the digital comparator 212 of the saturationdetermination unit 205 shown in FIG. 5.

In the ADC 330, the comparator 331 compares a reference voltage (lowvoltage Vcons) with the input voltage Vs1. Reversion of an output signalof the comparator 331 is used as a trigger, and, in response to thereversed output signal of the comparator 331, a digital code generatedin the 1-bit count 322 (e.g., 1 if input voltage is larger thanreference voltage and 0 if input voltage is smaller than referencevoltage) is latched into the counter 332 (latch unit).

The latched digital code is transferred by the horizontal transferscanning circuit 103 to the arithmetic control unit 340 for each column.Due to operations of the DAC 310, the counter controller 320, and theADC 330, an output corresponding to the output from the digitalcomparator 212 obtained by the counter 213 (FIG. 5) according to thesecond embodiment is obtained as an output of the horizontal transferscanning circuit 103.

With such a configuration, the arithmetic control unit 340 does not needto include the digital comparator 212 and has a configuration as shownin FIG. 9. The arithmetic control unit 340 includes an image signalprocessing unit 341, an illuminance calculation unit 342, a saturationdetermination unit 343, and an exposure control unit 344. The saturationdetermination unit 343 includes a counter 351 and a determination unit352.

The arithmetic control unit 340 is supplied with a digital code having avalue of 1 or 0 from the horizontal transfer scanning circuit 103. Thedigital code is supplied to the counter 351 of the saturationdetermination unit 343. The counter 351 counts the number of data itemswith the value of the digital code being 1. The determination unit 352determines whether or not the count value counted by the counter 351 isequal to or larger than the threshold value.

The processing of the counter 351 and the determination unit 352 isbasically the same as the processing of the counter 213 and thedetermination unit 214 in FIG. 5. That is, if the count value counted bythe counter 351 is equal to or larger than a set threshold value, thedetermination unit 352 determines that the saturation occurs due to thelong-term storage exposure.

A determination result of the determination unit 352 is supplied to theexposure control unit 344. If the determination unit 352 determines thatthe saturation occurs due to the long-term storage exposure, theexposure control unit 344 selects a short-term storage exposure controland starts exposure.

Otherwise, if the count value counted by the counter 351 is smaller thanthe set threshold value, the determination unit 352 determines that thesaturation does not occur due to the long-term storage exposure, and theexposure control unit 344 selects a long-term storage exposure controland starts exposure.

Such processing associated with the calculation of the illuminance inthe solid-state imaging device 300 will be described in detail withreference to a flowchart of FIG. 11. In Step S301, the counter 351 setsN=N+1. An initial value of N is 0, which is a value for identifying apixel to be processed (digital code to be processed). For example,numbers are assigned to pixels from an upper left pixel to a lower rightpixel of the pixel unit 101. When the value of N becomes one of thenumbers, a digital code of the pixel is set as a processing target.

In Step S302, whether or not a value of an Nth pixel is 1 is determined.The counter 351 is supplied from the horizontal transfer scanningcircuit 103 to the digital code having a value of 1 or 0. If thesupplied digital code is 1, the counter 351 increments a counter valueby one. If the supplied digital code is 0, the processing transitions toa subsequent digital code without counting.

That is, in Step S302, if it is determined that the value of the digitalcode as the processing target is 1, the processing proceeds to Step S303and the counter 351 updates a value to a value obtained by incrementingthe counter value by one.

After processing in Step S303 or in Step S302, if it is determined thatthe value of the digital code as the processing target is not 1, theprocessing proceeds to Step S304. In Step S304, whether or not N reachesthe number of pixels as the processing target is determined. In StepS304, if it is determined that N=target number of pixels is notestablished, the processing returns to Step S301 and the subsequentprocessing is repeated. That is, a subsequent pixel is set to be a pixelas the processing target and whether or not a value of a digital codefrom the pixel is 1 is determined.

Otherwise, in Step S304, if it is determined that N=target number ofpixels is established, the processing proceeds to Step S305. In StepS305, the determination unit 352 determines whether or not a count valuecounted by the counter 351 is equal to or larger than the thresholdvalue. The threshold value in the determination unit 352 is set to be,for example, the number of pixels as the processing target, in otherwords, 5% of the target number of pixels when it is determined thatN=target number of pixels is established by the processing in Step S304.

In Step S305, if it is determined that the count value is equal to orlarger than the threshold value, the processing proceeds to Step S306.In Step S306, a long storage/exposure time is set. In this case, it isdetermined that the saturation occurs due to the long-term exposure, andhence the processing proceeds to Step S306 and the long storage/exposuretime is set.

The determination unit 352 notifies the exposure control unit 344 of theselection of the long storage/exposure time. The exposure control unit344 controls read-out by the vertical scanning circuit 105 for the longstorage/exposure time. Thus, the illuminance calculation unit 342 issupplied with a long-term stored data item obtained when exposure isperformed for the long storage/exposure time. In Step S308, theilluminance calculation unit 342 obtains the long-term stored data item.Then, in Step S309, the illuminance calculation unit 342 calculates anilluminance based on Expression (1) above and outputs the illuminance tothe output control circuit 107.

Otherwise, in Step S305, if it is determined that the count value isequal to or larger than the threshold value or if it is determined thatthe saturation occurs due to the long-term exposure, the processingproceeds to Step S307. In Step S307, a short storage/exposure time isset.

The determination unit 352 notifies the exposure control unit 344 of theselection of the short storage/exposure time. The exposure control unit344 controls read-out by the vertical scanning circuit 105 for the shortstorage/exposure time. Thus, the illuminance calculation unit 342 issupplied with a short-term stored data item obtained when exposure isperformed for the short storage/exposure time. In Step S308, theilluminance calculation unit 342 obtains the short-term stored dataitem. Then, in Step S309, the illuminance calculation unit 342calculates an illuminance based on Expression (1) above and outputs theilluminance to the output control circuit 107.

Here, the processing associated with the calculation of the illuminancein the solid-state imaging device 300 will be described again withreference to FIG. 12. A point of time T11 to a point of time T12correspond to the first exposure time (long storage/exposure time). Adigital code obtained when exposure is performed for the first exposuretime is obtained by the counter 351 (FIG. 9) repeating the processing ofSteps S301 to S304.

At the point of time T12, a determination is made by the determinationunit 352. This processing corresponds to processing in Step S305. As aresult of making the determination at the point of time T12, which ofthe long storage/exposure time and the short storage/exposure time is tobe set is determined. If the short storage/exposure time is set (ifprocessing in Step S307 is executed), the data item obtained whenexposure is performed for the second exposure time (short storage time)from a point of time T13 to a point of time T14 is obtained.

If the determination unit 214 determines that the long storage time isto be set, the long storage/exposure time is set in the exposure controlunit 344 and the long-term stored data item is supplied to theilluminance calculation unit 342 (corresponding to processing in StepS306). The long-term stored data item supplied to the illuminancecalculation unit 342 at this time may be a long-term stored data itemobtained during the first exposure time from the point of time T11 tothe point of time T12 or may be a long-term stored data item obtainedduring the first exposure time from a point of time T15 to a point oftime T16.

The illuminance calculation unit 342 calculates an illuminance from thelong-term stored data item or the short-term stored data item andoutputs the illuminance (corresponding to processing in Steps S308 andS309). An output of the illuminance is performed at, for example, thepoint of time T16. At the point of time T16, both of the long-termstored data item and the short-term stored data item can be obtained,and hence an illuminance can be calculated even if either one of thelong-term stored data item and the short-term stored data item isselected.

Note that, if the long storage/exposure time is set, the obtention ofthe short-term stored data item performed between the point of time T13and the point of time T14 may be omitted. Alternatively, if the longstorage/exposure time is set and the long-term stored data item obtainedbetween the point of time T11 and the point of time T12 is used for theilluminance calculation, an illuminance may be calculated and outputbetween the point of time T12 and the point of time T13.

In this manner, the reference voltage (first threshold value) issupplied to the comparator 331 of the ADC 330. In the counter 332, thedigital code indicating whether or not it exceeds the first thresholdvalue is generated and counting is performed based on the digital codein the counter 351 of the saturation determination unit 343. Then,whether or not the count value counted by the counter 351 exceeds thesecond threshold value is determined by the determination unit 352.Thus, whether or not the saturation state occurs is determined.

By determining the saturation state in this manner, an illuminance canbe calculated with higher accuracy. Also in this case, as describedabove with reference to FIGS. 8A to 8C, an illuminance can be calculatedwithout using a data item obtained when the saturation occurs and theilluminance can be calculated with high accuracy. Further, according tosuch a system, the ADC operation that consumes large power is performedonly one time during either one of the long-term storage and theshort-term storage, and hence low power consumption can be achieved.

Although two data items of the long-term stored data item and theshort-term stored data item are used in the above description, aplurality of data items may be used. In this case, the exposure controlunit 344 is configured to be capable of controlling a plurality ofexposure times and the counter 351 is configured to obtain digital codesfrom data items when a control during one exposure time of the pluralityof exposure times is performed.

The digital code from the horizontal transfer scanning circuit 103 issupplied to the counter 351. As in the above-mentioned case, the numberof digital codes satisfying a predetermined condition, for example, acondition that the value is 1 is counted. Based on the count value, thedetermination unit 352 determines whether or not saturation occurs dueto the exposure time obtained when the digital code is obtained.

Depending on the determination result, for example, if it is determinedthat the saturation occurs, such that an illuminance is calculated usinga data item obtained during a different exposure time, the differentexposure time is set in the exposure control unit 344 and a storage dataitem obtained during the different exposure time is configured to beoutput to the illuminance calculation unit 342.

In this manner, the exposure control unit 344 may be capable ofcontrolling a plurality of exposure times and the determination unit 352may be configured to determine whether or not saturation occurs using atleast one data item of the plurality of data items obtained from theplurality of exposure times. Further, if it is determined that thesaturation occurs, a data item obtained during a different exposuretime, which is assumed to have been obtained without saturation, (dataitem obtained during exposure time different from exposure time whendata item used for determination is obtained) may be supplied to theilluminance calculation unit 342 and an illuminance may be calculated.

Fourth Embodiment

FIG. 13 is a diagram showing a configuration of a solid-state imagingdevice 400 according to a fourth embodiment. The solid-state imagingdevice 400 shown in FIG. 13 has a configuration obtained by combiningthe solid-state imaging device 200 shown in FIG. 5 with the solid-stateimaging device 300 shown in FIG. 9.

In the solid-state imaging device 400 shown in FIG. 13, a pixel unit101, a horizontal transfer scanning circuit 103, a vertical scanningcircuit 105, an output control circuit 107, an output control circuit108, a DAC 310, a counter controller 320, and an ADC 330 are the sameconfiguration as those of the solid-state imaging device 300 shown inFIG. 9, and hence will be denoted by the same reference symbols anddescriptions thereof will be omitted.

A basic configuration of an arithmetic control unit 410 is identical tothat of the arithmetic control unit 201 shown in FIG. 5. However, thearithmetic control unit 410 is different from the arithmetic controlunit 201 in that the arithmetic control unit 410 includes a switch thatselects generating a value counted by a counter 423 in the arithmeticcontrol unit 410 as in the arithmetic control unit 201 shown in FIG. 5or supplying a value as a digital code from the ADC 330 as in thearithmetic control unit 340 shown in FIG. 9.

Specifically, an arithmetic control unit 401 includes an image signalprocessing unit 411, a switch 412, a data selector 413, an illuminancecalculation unit 414, a saturation determination unit 415, and anexposure control unit 416. The saturation determination unit 415includes a switch 421, a digital comparator 422, the counter 423, adetermination unit 424, and a switch 425.

The switch 412 of the arithmetic control unit 410 is connected to theilluminance calculation unit 414 when receiving a digital code from theADC 330 and calculating an illuminance. Further, the switch 412 of thearithmetic control unit 410 is connected to the data selector 413 whenobtaining a long-term stored data item or a short-term stored data itemand calculating an illuminance based on a determination result from thedetermination unit 424.

The switch 425 of the saturation determination unit 415 is connected tothe exposure control unit 416 when receiving a digital code from the ADC330 and calculating an illuminance. Further, the switch 425 of thesaturation determination unit 415 is connected to the data selector 413when obtaining a long-term stored data item or a short-term stored dataitem and calculating an illuminance based on a determination result fromthe determination unit 424.

In this manner, the solid-state imaging device 400 shown in FIG. 13 iscapable of calculating an illuminance by switching between anilluminance calculation method by the solid-state imaging device 200shown in FIG. 5 (hereinafter, referred to as first illuminancecalculation) and an illuminance calculation method by the solid-stateimaging device 300 shown in FIG. 9 (hereinafter, referred to as secondilluminance calculation).

In the first illuminance calculation, the illuminance calculation isperformed as described above with reference to FIG. 5 to FIGS. 8A to 8C.In the second illuminance calculation, the illuminance calculation isperformed as described above with reference to FIG. 9 to FIG. 12. Whichof the first illuminance calculation and the second illuminancecalculation is to be used for performing the illuminance calculation canbe determined based on whether or not a predetermined condition issatisfied. The predetermined condition is, for example, shutter speedand the shutter speed changes between the first illuminance calculationand the second illuminance calculation.

Also as in the solid-state imaging device 400 shown in FIG. 13, theilluminance is calculated by the first illuminance calculation or thesecond illuminance calculation, and hence it is possible to calculate anilluminance with higher accuracy as in the above-mentioned case.

<Application to Back Side Illumination>

Each of the solid-state imaging device 100 according to the firstembodiment, the solid-state imaging device 200 according to the secondembodiment, the solid-state imaging device 300 according to the thirdembodiment, and the solid-state imaging device 400 according to thefourth embodiment that are described above can be applied to aback-side-illumination imaging device. Now, a description will be addedto the back-side-illumination imaging device.

FIG. 14 shows a configuration example of a back-side-illumination (BSI)CMOS-type solid-state imaging device. Here, portions corresponding tothree pixels are extracted and shown. A solid-state imaging device 500shown in FIG. 14 includes an on-chip micro lens 510, a color filterlayer 511, a photodiode layer 512, and a signal wiring layer 513 thatare stacked in this order from the upper side.

The on-chip micro lens 510 is an optical device for efficientlyconducting light to the photodiode layer 512. The color filter layer 511is a layer formed of organic molecules or pigments that selectivelytransmit, for example, visible wavelength components of three primarycolors (e.g., red, blue, green, or the like).

The photodiode layer 512 is a photoelectric conversion layer thatconverts received light into charge. Further, in the photodiode layer512, adjacent photodiodes are electrically isolated by an oxide film ofSTI (Shallow Trench Isolation) or the like or an EDI structure, a CIONstructure, or the like by implantation of impurities.

The signal wiring layer 513 is a layer in which wiring lines 520 forreading charge accumulated in the photodiode layer 512 are provided.

In this manner, in the solid-state imaging device 500, regarding thelight focused by the on-chip micro lens 510, a desired wavelengthcomponent is selected by the color filter layer 511 and then thetransmitted light reaches the photodiode layer 512. The transmittedlight is photoelectrically converted by the photodiode layer 512. Acarrier generated by the photoelectric conversion in the photodiodelayer 512 is output to an outside of the solid-state imaging device 500via the wiring lines 520 provided in the signal wiring layer 513, as animage signal.

The solid-state imaging devices 100, 200, 300, and 400 according to thefirst to fourth embodiments described above can be applied to theback-side-illumination solid-state imaging device 500 having theabove-mentioned configuration.

<Configuration of Imaging Apparatus>

The solid-state imaging devices 100, 200, 300, and 400 according to thefirst to fourth embodiments can form part of an imaging apparatus. FIG.15 is a block diagram showing an exemplary configuration of the imagingapparatus.

As shown in FIG. 15, an imaging apparatus 600 includes an optical system601, an imaging device 602, a signal processing circuit 603, a monitor604, and a memory 606. The imaging apparatus 600 is capable of capturingstill images and moving images. The optical system 601 includes a singlelens or a plurality of lenses. The optical system 601 guides image light(incident light) from a subject to the imaging device 602 and forms animage on a light receiving surface (sensor unit) of the imaging device602.

As the imaging device 602, the solid-state imaging device 100, 200, 300,or 400 including the pixel unit 101 having the above-mentionedconfiguration can be applied. Electrons are accumulated in the imagingdevice 602 for a predetermined period depending on the image formed onthe light receiving surface via the optical system 601. A signaldepending on the electrons accumulated in the imaging device 602 issupplied to the signal processing circuit 603.

The signal processing circuit 603 subjects signal charge output from theimaging device 602 to various types of signal processing. An image(image data item) obtained by the signal processing circuit 603performing the signal processing is supplied to the monitor 604 anddisplayed or supplied to the memory 606 and stored (recorded).

When the solid-state imaging device 100, 200, 300, or 400 having theabove-mentioned configuration is applied as part of the imaging device602 or the signal processing circuit 603, the imaging apparatus 600having the above-mentioned configuration can be controlled with anappropriate illuminance and an image quality is improved.

Further, the solid-state imaging devices 100, 200, 300, and 400according to the first to fourth embodiments of the present disclosurecan be employed for the above-mentioned back-side-illumination CMOS-typesolid-state imaging device, a front-side-illumination CMOS-typesolid-state imaging device, a CCD-type solid-state imaging device, andthe like.

Further, the solid-state imaging devices 100, 200, 300, and 400according to the first to fourth embodiments of the present disclosurecan be installed into imaging apparatuses such as a digital still cameraand a digital video camera as well as various electronic apparatusessuch as a cellular phone terminal and a personal computer.

<Recording Medium>

The above-mentioned sequence of processing can be executed by hardwareor software. If the sequence of processing is executed by software,programs configuring the software are installed into a computer. Here,the computer includes a computer incorporated in dedicated hardware and,for example, a generally-used personal computer that installs variousprograms to be able to execute various functions.

FIG. 16 is a block diagram showing an exemplary configuration ofhardware of a computer that executes the above-mentioned sequence ofprocessing by programs. In the computer, a CPU (Central Processing Unit)1001, a ROM (Read Only Memory) 1002, and a RAM (Random Access Memory)1003 are mutually connected via a bus 1004. To the bus 1004, furtherconnected is an input/output interface 1005. To the input/outputinterface 1005, connected are an input unit 1006, an output unit 1007, astorage unit 1008, a communication unit 1009, and a drive 1010.

The input unit 1006 includes a keyboard, a mouse, a microphone, and thelike. The output unit 1007 includes a display, a speaker, and the like.The storage unit 1008 includes a hard disk, a non-volatile memory, andthe like. The communication unit 1009 includes a network interface andthe like. The drive 1010 drives a removable medium 1011 such as amagnetic disc, an optical disc, a magneto-optical disk, and asemiconductor memory.

In the computer having the above-mentioned configuration, by the CPU1001 loading programs stored in, for example, the storage unit 1008 intothe RAM 1003 via the input/output interface 1005 and the bus 1004 andexecuting the programs, the above-mentioned sequence of processing isperformed.

The programs executed by the computer (CPU 1001) can be provided beingstored in the removable medium 1011, for example, as a package medium.Alternatively, the programs can be provided via a wired or wirelesstransmission medium such as a local area network, the Internet, anddigital satellite broadcasting.

In the computer, by mounting the removable medium 1011 on the drive1010, the programs can be installed into the storage unit 1008 via theinput/output interface 1005. Alternatively, the programs can be receivedby the communication unit 1009 and installed into the storage unit 1008via the wired or wireless transmission medium. Otherwise, the programscan be installed into the ROM 1002 or the storage unit 1008 in advance.

Note that the programs executed by the computer may be processed in timeseries based on the order described herein or processed at a necessarytiming, for example, when a call is made.

Herein, the system means an entire apparatus including a plurality ofapparatuses.

Note that the embodiments of the present disclosure are not limited tothe above-mentioned embodiments and may be variously changed withoutdeparting from the gist of the present disclosure.

Note that the present disclosure may also take the followingconfigurations.

(1) An imaging device, including:

an exposure control unit configured to control a plurality of exposuretimes;

a determination unit configured to determine whether or not saturationoccurs using at least one data item of a plurality of data itemsobtained during the plurality of exposure times; and

an illuminance calculation unit configured to calculate, if thedetermination unit determines that the saturation occurs, an illuminanceusing a data item different from the at least one data item used in thedetermination.

(2) The imaging device according to Item (1), in which

the determination unit is configured to calculate an average value ofthe plurality of data items and determine, based on a comparison resultbetween the average value and a threshold value, whether or notsaturation occurs.

(3) The imaging device according to Item (1), in which

the determination unit is configured to calculate an average value ofdata items obtained during a first exposure time and determines, if theaverage value is equal to or larger than a threshold value, that thesaturation occurs, and

the illuminance calculation unit is configured to obtain, if thedetermination unit determines that the saturation occurs, a data itemobtained during a second exposure time shorter than the first exposuretime, and calculate an illuminance.

(4) The imaging device according to any one of Items (1) to (3), furtherincluding:

a comparator configured to compare each of the plurality of data itemswith a first threshold value; and

a count unit configured to count the number of comparison results ofcomparison results from the comparator, each of which satisfies apredetermined condition, in which

the determination unit is configured to determine, based on a comparisonresult between a count value of the count unit and a second thresholdvalue, whether or not saturation occurs.

(5) The imaging device according to any one of Items (1) to (3), furtherincluding:

a comparator configured to compare each of data items obtained during afirst exposure time with a first threshold value; and

a count unit configured to count the number of comparison results ofcomparison results from the comparator, in each of which the data itemis equal to or larger than the first threshold value, in which

the determination unit is configured to determine, if a count value ofthe count unit is equal to or larger than a second threshold value, thatthe saturation occurs, and

the illuminance calculation unit is configured to obtain, if thedetermination unit determines that the saturation occurs, a data itemobtained during a second exposure time shorter than the first exposuretime, and calculate an illuminance.

(6) The imaging device according to any one of Items (1) to (5), furtherincluding:

a comparator configured to compare each of the plurality of data itemswith a first threshold value;

an output unit configured to output, as a comparison result from thecomparator, codes each indicating a comparison result between the dataitem and the first threshold value; and

a count unit configured to count the number of codes of the codes fromthe output unit, each of which satisfies a predetermined condition, inwhich

the determination unit is configured to determine, based on a comparisonresult between a count value of the count unit and a second thresholdvalue, whether or not saturation occurs.

(7) The imaging device according to any one of Items (1) to (5), furtherincluding:

a comparator configured to compare each of data items obtained during afirst exposure time with a first threshold value;

an output unit configured to output, as a comparison result from thecomparator, codes each indicating whether or not the data item is equalto or larger than the first threshold value; and

a count unit configured to count the number of codes of the codes fromthe output unit, each of which indicates that the data item is equal toor larger than the first threshold value, in which

the determination unit is configured to determine, if a count value ofthe count unit is equal to or larger than a second threshold value, thatthe saturation occurs, and

the illuminance calculation unit is configured to obtain, if thedetermination unit determines that the saturation occurs, a data itemobtained during a second exposure time shorter than the first exposuretime, and calculate an illuminance.

(8) An imaging method for an imaging device including an exposurecontrol unit, a determination unit, and an illuminance calculation unit,the method including:

controlling, by the exposure control unit, a plurality of exposuretimes;

determining, by the determination unit, whether or not saturation occursusing at least one data item of a plurality of data items obtainedduring the plurality of exposure times; and

calculating, by the illuminance calculation unit, if the determinationunit determines that the saturation occurs, an illuminance using a dataitem different from the at least one data item used in thedetermination.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

What is claimed is:
 1. An imaging device, comprising: a plurality ofpixels that respectively output analog signals in response to incidentlight; a plurality of signal lines respectively connected to theplurality of pixels; a plurality of A/D converters respectivelyconnected to the plurality of signal lines, the plurality of A/Dconverters configured to convert the analog signals into respectivedigital signals; an illuminance calculation unit configured to calculaterespective illuminances corresponding to the digital signals.
 2. Theimaging device according to claim 1, further comprising: an exposurecontrol unit configured to control a plurality of exposure times.
 3. Theimaging device according claim 1, further comprising: a determinationunit configured to convert a determination signal and output thedetermination signal to the illuminance calculation unit.
 4. The imagingdevice according to claim 3, wherein the determination unit compares atleast one of the digital signals and a threshold value to determinewhether or not saturation occurs.
 5. The imaging device according toclaim 4, wherein the determination unit is configured to calculate anaverage value of at least some of the digital signals and determine,based on a comparison result between the average value and the thresholdvalue, whether or not saturation occurs.
 6. The imaging device accordingto claim 4, wherein the determination unit is configured to calculate anaverage value of at least some of the digital signals obtained during afirst exposure time and to determine, if the average value is equal toor larger than the threshold value, that the saturation occurs.
 7. Theimaging device according to claim 6, wherein the illuminance calculationunit is configured to obtain, if the determination unit determines thatthe saturation occurs, at least one of the digital signals obtainedduring a second exposure time shorter than the first exposure time, andto calculate therefrom a corresponding illuminance.
 8. The imagingdevice according to claim 3, further comprising: at least one comparatorconfigured to compare the digital signals with a first threshold value;and a count unit configured to count a number of comparison results fromthe comparator, each of which satisfies a predetermined condition,wherein the determination unit is configured to determine, based on acomparison result between a count value of the count unit and a secondthreshold value, whether or not saturation occurs.
 9. The imaging deviceaccording to claim 3, further comprising: at least one comparatorconfigured to compare the digital signals obtained during a firstexposure time with a first threshold value; and a count unit configuredto count a number of comparison results from the comparator, in each ofwhich a given one of the digital signals is equal to or larger than thefirst threshold value, wherein the determination unit is configured todetermine, if a count value of the count unit is equal to or larger thana second threshold value, that the saturation occurs, and theilluminance calculation unit is configured to obtain, if thedetermination unit determines that the saturation occurs, at least oneof the digital signals during a second exposure time shorter than thefirst exposure time, and to calculate an illuminance.
 10. The imagingdevice according to claim 3, further comprising: at least one comparatorconfigured to compare the digital signals with a first threshold value;an output unit configured to output, as a comparison result from thecomparator, codes respectively indicating a comparison result betweenthe digital signals and the first threshold value; and a count unitconfigured to count a number of codes of the codes from the output unit,each of which satisfies a predetermined condition, wherein thedetermination unit is configured to determine, based on a comparisonresult between a count value of the count unit and a second thresholdvalue, whether or not saturation occurs.
 11. The imaging deviceaccording to claim 3, further comprising: at least one comparatorconfigured to compare the digital signals obtained during a firstexposure time with a first threshold value; an output unit configured tooutput, as a comparison result from the comparator, codes respectivelyindicating whether or not the digital signals are equal to or largerthan the first threshold value; and a count unit configured to count anumber of codes of the codes from the output unit, each of whichindicates that a given one of the digital signals is equal to or largerthan the first threshold value, wherein the determination unit isconfigured to determine, if a count value of the count unit is equal toor larger than a second threshold value, that the saturation occurs, andthe illuminance calculation unit is configured to obtain, if thedetermination unit determines that the saturation occurs, at least oneof the digital signals obtained during a second exposure time shorterthan the first exposure time, and calculate an illuminance.